Cross-corrugated, sheet metal structured packings have gained a considerable portion of the distillation column internals business since coming into widespread commercial use approximately fifteen years ago. These structured packings are commonly recognized as being more efficient than random packings, based on their lower pressure drop per theoretical stage of separation. They have also replaced trays in some applications, primarily because of their higher capacity in a given column diameter, at least at low to medium liquid rates.
One industry where structured packings have had a major impact is the cryogenic air separation industry. The primary advantage of structured packings in cryogenic air separation is that the pressure drop over the columns may be an order of magnitude lower than when using the previous column internals of choice in cryogenic air separation columns, which were trays. This reduces the operating pressure of the columns, which in turn drops the pressure to which air must be compressed and thus the power requirements for the plant.
Meier (U.S. Pat. No. 4,296,050) describes the majority of structured packings sold commercially to this point, which are cross-corrugated sheets containing both apertures and fluting (a form of surface texture). Since the nearly twenty years since this patent, numerous attempts to improve on the basic structure of the structured packing have been published. However, none appear to have had a significant commercial impact until Billingham et al. (U.S. Pat. No. 5,632,934). It was recognized in this patent that flooding of structured packings was initiated at the interface between layers and that this bottleneck could be removed by reducing the pressure drop of gas in the base of each brick. Since the issuance of this patent, two products have been commercialized that use the ideas put forward in this patent.
It would be desirable to have structured packing which will improve the mass transfer achieved for a given pressure drop by minimizing pressure losses that are not efficient in promoting mass transfer, thereby resulting in the use of smaller distillation columns.
Accordingly, it is an object of this invention to provide corrugated structured packing, having an improvement over conventional corrugated structured packing, which enables separation such as cryogenic rectification to be carried out over a reduced column height.